This research is aimed at elucidating the mechanisms by which tissues adjust their blood flow to meet their metabolic demands. Major effort is being expended in investigating the participation of oxygen in this regulatory process. The microvessels of epithelial tissues (hamster cheek pouch) and striated muscle tissue are observed during various challenges to the regulatory process ( e.g., functional hyperemia of exercise, reactive hyperemia and oxygen deprivation) and concentrations of oxygen at various tissue sites are measured using microsensors. The delivery of oxygen is assessed using spectrophotometric methods to determine the oxygen saturation of the microvessel blood. Substantial effort is devoted to describing the microvascular patterns and the various control sites during the regulatory responses.